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Abnormal secondary growth
This document discusses abnormal or anomalous secondary growth in plants. It defines secondary growth as an increase in plant girth due to vascular cambium or cork cambium. Anomalous secondary growth does not follow the normal pattern of a single vascular cambium producing xylem internally and phloem externally. Some examples given of plants that exhibit anomalous secondary growth include Bougainvillea, which forms multiple cambium rings outside the oldest phloem, and monocots like Dracaena which can exhibit secondary growth in roots. The document also describes different types of anomalous secondary growth that can occur in dicot stems due to abnormal cambium position or activity.
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Abnormal secondary growth
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- 2. Secondary Growth Anincrease in plant girth due to vascular cambium or cork cambium is called secondary growth.
- 3. Secondary growth &lateral meristems
- 4. Anomalous Whereas thedevelopment, arrangement, activity of the vascular cambium in most woody dicotyledonous and Gymnospermous plants tends to be very similar, there are some alternatives which produce new secondary tissues that do not follow a normal pattern. As a result, the secondary plant structures that are formed are termed anomalus. Most anomalous growth is associated with the formation of multiple cambia.`
- 5. Abnormal Secondary growth Abnormal secondary growth does not follow the pattern of a single vascular cambium a thick hair clit producing xylem to the inside and phloem to the outside. Some dicots have anomalous secondary growth, e.g. in Bougainvillea a series of cambia arise outside the oldest phloem.
- 7. Abnormal growth inmonocot Most monocots either have no secondary growth or else anomalous secondary growth of some type;
- 8. Monocotyledons Dracaena (the Dragon'sblood tree) is the only monocot which has been shown to also have secondary growth in roots.
- 9. Anomalous secondary growthin dicot system Secondary growth in dicot systems characterized by the following;
- 10. By theformation of new cambium strips in the interfascicular region by the initiation of meristematic activity in the parenchymatous cells of primary medullar rays adjacent to fascicular cambium. These interfascicular cambium strips join with the fascicular cambium to from a complete ring of vascular cambium. Position of vascular cambium ring always lies between the primary xylem and phloem.
- 11. Cells ofthis cambium cut secondary xylem towards inner side and secondary phloem towards outer side. Normally single vascular cambium ring remains active and no extra cambium rings are formed except a ring of cork cambium which develops extra stellar.
- 12. Anomalous SecondaryGrowth: type of secondary growth which deviates from the normal type is regards as abnormal or anomalous secondary growth. In Dicot stem anomalous secondary growth occurs due to following reasons – Normal position of cambium with abnormal activity. Abnormal position of cambium with normal activity. Abnormal position of cambium with abnormal activity
- 13. Abnormal secondary growthin dicot stem Cross section of Boerhaavia stem, showing successive rings of xylem and phloem
- 14. Abnormal secondary growthin different plants Beta vulgaris root & stem. Beta TS root
- 15. Abnormal secondary grothin plants Bougainvillea is a member of the Nyctaginaceae and is an example of a dicotyledonous stem which displaysanomalous secondary growth. In this TS, near the centre of the stem, you will see some primary vascular bundles embedded in lignified pith parenchyma. Move the slide towards the outer regions, and you will notice that there has been fairly extensive production of secondary vascular tissue. Look for the vascular cambium. Secondary phloem and secondary xylem lie on either side of it. The secondary xylem is composed of tracheids, fibers and narrow- diameter vessels. Interspersed with the secondary xylem you will be able to see small pockets of phloem and what look like large- diameter of metaxylum.
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